Hydrogen generation apparatus and method for using same

ABSTRACT

A compact hydrogen generator for use with fuel cells and other applications includes a hydrogen membrane reactor having a combustion chamber and a reaction chamber. The two chambers are have a fluid connection and a heat exchange relationship with one another. The hydrogen generation apparatus also includes a fuel supply, a fuel supply line for transporting fuel from the fuel supply to the reaction chamber, an oxygen supply, an oxygen supply line for transporting oxygen form the oxygen supply to the combustion chamber, as well as a tail gas supply line for transporting tail gas supply line for transporting tail gases form the reaction chamber, a combustion by-product line for transporting combustion by-products for the combustion chamber, and a reaction product line for transporting hydrogen from the reaction chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase Application of InternationalApplication Number PCT/US02/12822, filed Apr. 23, 2002, entitled“Hydrogen generation apparatus and method for using same” by ApplicantMesosystems Technology Inc*-., now expired, which claims the benefit ofthe prior filing date of U.S. Provisional Patent Application No.60,286,114, filed Apr. 23, 2001, now expired, the disclosures of whichare incorporated herein by reference in their entirety.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT

This invention was made under contract with the United States ArmyResearch Office, under Contract No. DAAD19-01-C-0015, and the UnitedStates Government may have certain rights in the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to the chemical arts. Moreparticularly, the present invention relates to an apparatus and methodfor generating hydrogen gas by decomposing or reforming a liquid fuel.

2. General Background and State of the Art

The growing popularity of portable electronic devices has produced anincreased demand for compact and correspondingly portable electricalpower sources to energize these devices. Developments in robotics andother emerging technology applications are further increasing the demandfor small, independent power sources.

At present, storage or rechargeable batteries are typically used toprovide independent electrical power sources for portable devices.However, the amount of energy that can be stored in storage orrechargeable batteries is insufficient to meet the need of certainapplications.

Hydrogen/air fuel cells (H/AFCs) have enormous potential as areplacement for batteries. Because they can operate on very energy-densefuels, fuel cell-based power supplies offer high energy-to-weight ratioscompared with even state-of-the-art batteries. Fuel cells are ofparticular interest to the military, where significant efforts are beingmade to reduce the weight of power supplies that soldiers must carry tosupport high-tech, field-portable equipment. There is also considerablepotential for utilizing fuel cell-based power supplies for commercialapplications, particularly where small size and low weight aredesirable.

A common H/AFC is a polymer electrolyte membrane (PEM) fuel cell. PEMfuel cells are constructed of an anode and a cathode separated by apolymer electrolyte membrane.

Functionally, fuel cells generate electricity by reacting hydrogen withoxygen to produce water. Since oxygen can typically be obtained from theambient atmosphere, only a source of hydrogen must be provided tooperate a fuel cell. Merely providing compressed hydrogen is not alwaysa viable option, because of the substantial volume that even a highlycompressed gas occupies. Liquid hydrogen, which occupies less volume, isa cryogenic liquid, and a significant amount of energy is required tomaintain the extremely low temperatures required to maintain it as aliquid. Furthermore, there are safety issues involved with the handlingand storage of hydrogen in the compressed gas form or in the liquidform.

Several alternative approaches are available. These alternatives includeammonia decomposition and hydrocarbon reformation. Ammonia decompositionis relatively easy. Ammonia can be thermo-catalytically cracked atrelatively low temperatures to produce a gas mixture that is 75%hydrogen by volume. Hydrocarbon fuels are somewhat more technicallychallenging, because hydrocarbon reformation requires relatively highertemperatures, and the simple cracking of hydrocarbons produces a solidresidue which is undesirable in a fuel cell application. However, thereformation of hydrocarbon fuels offers the incentive of enabling ahigher energy density fuel to be used, as compared with the use ofammonia as a fuel source, i.e., the production of a greater mass ofhydrogen per unit mass of fuel. Consequently, there is a desideratum foran apparatus that has the flexibility to effectively and efficientlygenerate hydrogen from either ammonia or hydrocarbon fuel.

The ammonia decomposition reaction can be represented as follows:2NH₃→N₂+2H₂  (1)

The simple hydrocarbon cracking reaction can be represented as follows:C_(n)H(2_(n)+2)→C_(n(solid))+(n+1)H₂  (2)

The formation of solid residues can be avoided through the use ofoxidative cracking processes or by employing steam reforming. Oxidativecracking be represented as follows:C_(n)H(2_(n)+2)_(n)O₂→_(n)CO₂+(n+1)H₂  (3)

Steam reforming can be represented as follows:C_(n)H(2_(n)+2)2_(n)H₂O→_(n)CO₂+(3_(n)+1)H₂  (4)

It is a drawback of ammonia decomposition that traces of un-reactedammonia (typically <2000 ppm) remain in the product gas stream. One ofthe challenges of utilizing ammonia to produce hydrogen for a fuel cellis that H/AFCs do not tolerate ammonia in the hydrogen feed gas, so thetrace amounts of ammonia in the hydrogen produced by an ammonia crackermust be removed before the remaining H₂/N₂ mixture is supplied to a fuelcell.

It is a drawback of hydrocarbon reformulation that the actual product isa mixed gas stream that contains substantial amounts of carbon monoxide(CO). Furthermore, the product is a gas stream that also containspartially oxidized hydrocarbons. Both carbon dioxide and partiallyoxidized hydrocarbons can poison the anode electro-catalysts used in PEMfuel cells. Thus, utilizing either ammonia decomposition, oxidativecracking or steam reforming requires additional steps to purify thehydrogen, or decompose the impurities. Such additional processes addsize, cost, and complexity to a hydrogen generation system, makingachieving a compact, low cost, and portable system more difficult.Therefore, it is also a desideratum to provide a hydrogen generationsystem that can be used to provide hydrogen to a fuel cell, whichrequires minimal or no additional processing to purify the hydrogen thatis produced before such hydrogen can be used in a fuel cell.

To compete with battery-based power supplies, such an H/AFC apparatusneeds to be compact and reliable. It is a further desideratum to developa portable hydrogen supply with a volume less than 1 liter and a massless than 1 kg that can produces up to 50 watts of electrical power,with a total energy output of 1 kWh. Commercially available metalhydride storage cylinders are available in 920 gm cylinders that containthe equivalent of 100 W-h of hydrogen;

thus, a total energy output of 1 kWh represents an order of magnitudeincrease in energy density over commercially available apparatuses.

SUMMARY OF THE INVENTION

Now in accordance with this invention there has been found a compacthydrogen generation apparatus for use with fuel cells and otherapplications. The hydrogen generator includes a hydrogen membranereactor having a combustion chamber and a reaction chamber. The twochambers are have a fluid connection and a heat exchange relationshipwith one another. The hydrogen membrane reactor also includes a fuelinlet into the reaction zone, an oxygen inlet into the combustionchamber, a tail gas outlet out of the reaction zone, a hydrogen outletout of the hydrogen exhaust zone, and a by-product outlet out of thecombustion chamber.

The hydrogen generation apparatus also includes a fuel supply, a fuelsupply line for transporting fuel from the fuel supply to the reactionchamber, an oxygen supply, an oxygen supply line for transporting oxygenfrom the oxygen supply to the combustion chamber, as well as a tail gassupply line for transporting tail gases from the reaction chamber, acombustion byproduct line for transporting combustion by-products fromthe combustion chamber, arid a reaction product line for transportinghydrogen from the reaction chamber.

In some embodiments, the hydrogen membrane reactor is formed of a topplate, a bottom plate, and a separation plate having first and secondopposing surfaces. The top plate and the first surface of the separationplate together define the reaction chamber, while the bottom plate andthe second surface of the separation plate together define thecombustion chamber. A hydrogen separation membrane having first andsecond opposing surfaces is disposed between the top plate and theseparation plate, so that the top plate and the first surface of thehydrogen separation membrane together define a hydrogen exhaust zone,while the separation plate and the second surface of the hydrogenseparation membrane together defining a reaction zone. In theseembodiments, the fuel supply line transports fuel to the reaction zone,the tail gas supply line transports tail gas from the reaction zone, andthe reaction product line transports hydrogen from the hydrogen exhaustzone.

And in some embodiments, the combustion chamber has a plurality ofcombustion channels extending radially from the surface of theseparation plate and forming a fluid path through the combustionchamber, the hydrogen exhaust zone has a plurality of hydrogen exhaustchannels extending radially from the first surface of the hydrogenmembrane and forming a fluid path through the hydrogen exhaust zone, andthe reaction zone has a plurality of reaction channels extendingradially from the second surface of the hydrogen membrane and forming afluid path through the reaction zone. The height and width of each ofthe combustion channels, the hydrogen exhaust channels, and the reactionchannels is preferably between 0.01 mm and 10 mm and more preferablybetween 0.5 mm and 5 mm.

In some embodiments, the tail gas supply line makes a direct fluidconnection between the reaction zone and the combustion chamber. Inother embodiments, the tail gas supply line makes an indirect fluidconnection between the reaction zone and the combustion chamber via theoxygen supply line.

Some embodiments additionally include a fuel heat exchanger operablyconnected to the fuel supply line and one of the combustion by-productline or the reaction product line. In preferred embodiments, the fuelheat exchanger is operably connected to the combustion byproduct line.Some embodiments additionally include an oxygen heat exchanger operablyconnected to the oxygen supply line and one of the combustion by-productline or the reaction product supply line. In preferred embodiments, theoxygen heat exchanger is operably connected to the reaction productline.

In preferred embodiments, the fuel heat exchanger and/or the oxygen heatexchanger are counterflow-type heat exchangers. In more preferredembodiments, the fuel heat exchanger and/or the oxygen heat exchangerare stacked-plate-type heat exchangers having channels with a height anda width between about 0.01 mm and 10 mm running between the stackedplates.

Some embodiments additionally include a hydrogen reservoir in fluidconnection with the reaction product supply line. A hydrogen fuel cellin fluid connection with the reaction product supply line is included insome embodiments.

In some embodiments, a combustion catalyst in included the combustionchamber. The combustion catalyst and the reaction catalyst can be packedin or coated on the internal surfaces of the combustion and/or reactionchannels, respectively.

In some embodiments, the fuel supply is an ammonia supply. Theseembodiments can additionally include an ammonia adsorbent supply influid communication with the reaction product line.

In other embodiments, the fuel supply is a hydrocarbon supply Suitablehydrocarbon fuel supplies include methanol, propane, butane, andkerosene fuel supplies.

Also in accordance with the invention there has been found a method forgenerating hydrogen. In a first step a hydrogen-producing fuel is flowedthrough the reaction zone and into the combustion chamber of thehydrogen membrane reactor. The reaction zone contains a reactioncatalyst initially at a temperature less than the reaction catalyst'slight-off temperature. In preferred embodiments, the light offtemperature of the reaction catalyst is less than 6500 C. Suitablereaction catalysts include ruthenium catalysts, nickel catalysts, ironoxide catalysts, rhodium catalysts, iridium catalysts or rheniumcatalysts.

The hydrogen-producing fuel is then combusted to produce combustionby-products while raising the temperature of the reaction catalyst inthe reaction zone and the combustion by-products are exhausted.Combustion of the hydrogen-producing fuel is continued for a period oftime sufficient to raise the temperature of the reaction catalyst toabove its light off temperature.

Additional hydrogen-producing fuel is flowed into the reaction chamberand reacted to produce hydrogen and tail gases. The hydrogen is thenseparated from the tail gases by selectively passing the hydrogenthrough the hydrogen membrane.

In some embodiments, the combustion chamber contains a combustioncatalyst having a light-off temperature. In preferred embodiments, thecombustion catalyst also has a light off temperature of less than 650°C. Suitable combustion catalysts include platinum-rhodium catalysts.

In some embodiments, the tail gas is recirculated from the reaction zoneinto the combustion chamber. In some embodiments, the hydrogen-producingfuel is pre-heated prior to flowing the hydrogen producing fuel into thereaction zone. And some embodiments include flowing oxygen, preferablypre-heated oxygen into the combustion chamber.

In some embodiments, the separated hydrogen is flowed into a hydrogenreservoir. In other embodiments the separated hydrogen is flowed into ahydrogen fuel cell.

In some embodiments, the hydrogen-producing fluid is ammonia. And issome of these embodiments, the separated hydrogen is flowed through anammonia adsorbent. In other embodiments, the hydrogen-producing fluid isa hydrocarbon. Preferred hydrocarbons include methanol, propane, butane,and kerosene.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a block diagram illustrating the primary components of ahydrogen generator in accordance with the present invention;

FIG. 2 is a schematic view of a hydrogen membrane reactor and relatedcomponents for use in accordance with the present invention;

FIG. 3 is a cross-sectional view of a hydrogen membrane reactor inaccordance with the present invention;

FIG. 4 is an exploded isometric view of the different layers of thehydrogen membrane reactor of FIG. 3;

FIG. 5 is an exploded isometric view of heat exchanger for use in oneembodiment of the hydrogen reactor in accordance with the presentinvention;

FIG. 6 is a block diagram corresponding to the hydrogen membrane reactorof FIG. 1, showing the system during a start up sequence;

FIG. 7 is a block diagram corresponding to the hydrogen membrane reactorof FIG. 1, showing the system during a steady state sequence;

FIG. 8 is a block diagram illustrating the primary components of analternative hydrogen generator in accordance with the present invention;

FIG. 9 is a block diagram corresponding to the hydrogen membrane reactorof FIG. 8, showing the system during a start up sequence;

FIG. 10 is a block diagram corresponding to the hydrogen membranereactor of FIG. 8, showing the system during a steady state sequence;

FIG. 11 is a block diagram illustrating the primary components of asecond alternative hydrogen generator in accordance with the presentinvention;

FIG. 12 is a block diagram illustrating the primary components of athird alternative hydrogen generator in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Particular embodiments of the invention are described below inconsiderable detail for the purpose for illustrating its principles andoperation. However, various modifications may be made, and the scope ofthe invention is not limited to the exemplary embodiments described.

It is an advantage of the hydrogen generators in accordance with theinvention, that with only minor modifications they can be used togenerate hydrogen from either ammonia or hydrocarbon fuels.Representative hydrocarbon fuels include, methanol, propane, butane,gasoline, and kerosene fuels, such as JP-8.

The fuel must be capable of both generating hydrogen and providingthermal energy. In preferred embodiments, the fuel is a liquid fuel. Forexample, while ammonia is a gas at standard temperature and pressure(STP) conditions, the ammonia is preferably stored in a liquid state.The ammonia is easily liquefied by compression (114 pounds per squareinch) and/or by cooling to about −33° C. Similarly, while solidhydrocarbons are available, the use of a liquid hydrocarbon fuel greatlysimplifies fuel transport. As with ammonia, hydrocarbons that aregaseous at STP (such as propane) are conventionally stored andtransported as liquefied gases. Consequently, in preferred embodiments,the fuel is either a material that is a liquid at STP or a liquefiedgas.

The hydrogen generator should preferably incorporate a relatively small,efficient hydrogen membrane reactor characterized by having excellentheat and mass transfer rates, and adapted to operate at a relatively lowreaction temperature (so that conventional materials can be used forfabricating reactor components). The reactor includes two chambers, areaction chamber, followed by a combustion chamber. The two chambers arearranged in close proximity and are in a heat exchange relationship withone another. The hydrogen membrane is in fluid communication with thehydrogen generating reaction chamber. Each chamber preferablyincorporates highly active catalysts characterized by having rapidresidence times and excellent heat transfer abilities with respect tothe reactor (to enable a minimal volume reactor to be employed). Thesystem further includes a pair of lightweight recuperative heatexchangers characterized as having meso-dimensioned channels and veryhigh heat transfer rates, as well as extremely efficient insulation thatminimizes reactor and heat exchanger heat loss into the environment.

A fuel supply is provided, as well as an oxygen supply, e.g., an ambientair intake, and an exhaust. The hydrogen produced can be routed to anoptional PEM fuel cell, a storage tank or other hydrogen usingapparatus. Hydrogen fuel generators employing ammonia as the fuel mayfurther incorporate an ammonia adsorbent supply in fluid communicationwith a hydrogen reaction product line exiting the hydrogen membranereactor to remove trace ammonia that could poison a fuel cell or have anadverse effect on the fuel cell. Hydrocarbon fueled embodimentspreferably include a water storage tank, a water/fuel pump, an ambientair pump, and optionally a steam recovery vessel. By minimizingcomponent size, a larger proportion of the system can be dedicated tothe volume of fuel ammonia supplied, thereby increasing the amount ofhydrogen that can be generated for each tank of ammonia fuel.

An exemplary ammonia-based hydrogen generator 10 is shown in FIG. 1. Thehydrogen generator includes a hydrogen membrane reactor 12 having twoseparate chambers, a reaction chamber 13 a in a heat exchangerelationship with a combustion chamber 13 b (as shown in FIGS. 2-4), afuel supply 14, an oxygen supply 16, and a hydrogen reservoir 18.

Appropriate fluid lines are included as shown, and arrowheadsincorporated into such fluid lines indicate the proper flow of fluidthrough the hydrogen generator. The fluid lines include a fuel supplyline 20 for transporting fuel from the fuel supply 14 to the reactionchamber 13 a, an oxygen supply line 22 for transporting oxygen from theoxygen supply 16 to the combustion chamber 13 b, a tail gas supply line23 for transporting tail gases from the reaction chamber and directly orindirectly into the combustion chamber, a combustion byproduct line 24for exhausting the combustion by-products from the combustion chamber,and a reaction product line 26 for transporting hydrogen from thereaction chamber to the hydrogen reservoir 18. While the tail gas supplyline is shown external to the reactor, in some embodiments, the tail gassupply line is placed within an insulated region inside the reactor, sothat heat loss does not occur as the tail gas is transported from thereaction chamber to combustion chamber.

In those embodiments where the fuel is a liquefied gas such as ammoniaor propane, stored under pressure, no pumping system is required to thefuel through fuel supply line 20, through the fuel heat exchanger 28,and into the hydrogen membrane reactor 12. However, in embodiments wherethe fuel is a liquid such as JP-8 a separate pumping system (not shown)must be employed.

Especially in embodiments where a maximum energy density is desired,proper management of thermal energy is critical. Fuel in the fuel supply14 is used both to provide the thermal energy needed to drive thehydrogen-production reaction, as well as a feedstock in the reaction.Thus, every gram of fuel used to generate thermal energy is a gram thatis unavailable to be used as feedstock. If less feedstock is available,the energy density of the system is reduced. Accordingly, in someembodiments, a fuel heat exchanger 28 and an oxygen heat exchanger 30are employed to make efficient use of the thermal energy available tothe system. In some embodiments, the hydrogen membrane reactor 12, thefuel heat exchanger 28, and the oxygen heat exchanger 30, are allintegrated into a single component.

While, one exemplary use of the inventive hydrogen generator is togenerate hydrogen to be used in an H/AFC 31, such a system can bebeneficially employed to generate hydrogen for other purposes as well.For example, the generator can be used as a source of hydrogen forwelding or metal treating. Thus, the fuel cell is shown as an optionalcomponent.

In general, the physical size of each of the functional elements of ahydrogen generator in accordance with the invention depends on thedesired size and capacity of the hydrogen generator. In one preferredembodiment, the hydrogen generator is less than 1 liter in volume and 1kilogram in mass. In such an embodiment, the individual size of eachelement is critical in obtaining a hydrogen generator that issufficiently compact. In other embodiments, the exact size of the systemis not critical, though a compact design is typically to be preferred.In general, the size of components such as the fuel supply 14 and thehydrogen reservoir 18 will be a function of the amount of power requiredand a maximum desired time interval between replenishing systemconsumables. For example, the fuel supply must provide a sufficientquantity of fuel to ensure that performance goals for the intendedperiod of operation are achieved.

With respect to the hydrogen membrane reactor 12, the fuel heatexchanger 28, and the oxygen heat exchanger 30, these elements arepreferably as compact and light-weight as practical. Especially forembodiments in which the overall system size is of concern, minimizingthe size and weight of the hydrogen membrane reactor, the fuel heatexchanger, and the air heat exchanger enables a greater proportion ofsystem size and weight to be dedicated to fuel storage, therebyincreasing the energy density and/or operating interval betweenrefueling of the system.

It should be understood that while in at least one embodiment of thepresent invention, a preferred reactor will be fabricated as small andcompact as feasible, hydrogen membrane reactors in accordance with thepresent invention can be scaled up to a larger size capable ofgenerating significantly larger volumes of hydrogen, if desired.Similarly, such an exemplary hydrogen membrane reactor can be employedin hydrogen generating systems using large fuel supplies, to achieve ahydrogen generator that can provide modest volumes of hydrogen to a fuelcell (or other apparatus) for extended periods of time.

Some of the features of a preferred embodiment of the hydrogen membranereactor 12 are shown in FIG. 2. The reactor includes a top plate 32, abottom plate 34, and a separation plate 36 having first and secondopposing surfaces 37 a and 37 b, respectively. The top plate and thefirst surface of separation plate together define the reaction chamber13 a, while the bottom plate and the second surface of the separationplate together define the combustion chamber 13 b.

The separation plate 36 is preferably a thin metal plate having a highthermal conductivity. High thermal conductivity is critical, as heatgenerated within the combustion chamber must be available to provide therequired temperature conditions within the hydrogen generating reactionchamber. The top plate 32 and the bottom plate 34 are structural and donot need to be thermally conductive.

Disposed between the top plate 32 and the separation plate 36 is ahydrogen separation membrane 38. The hydrogen separation membraneenables the hydrogen to be separated from the other decomposition orreformation reaction products. Such membranes allow hydrogen to diffuseacross (through) the membrane, while preventing the other reactionproducts from crossing the membrane. Such membranes are commerciallyreadily available.

The hydrogen separation membrane 38 has first and second opposingsurfaces 39 a and 39 b, respectively, spanning the width of the reactor.The top plate 32 and the first surface together define a hydrogenexhaust zone 40, while the separation plate 36 and the second surfacetogether define a reaction zone 41.

In an alternative embodiment, a hydrogen separation membrane 38 that issubstantially smaller hydrogen separation membrane is employed. Whenammonia is used as the fuel, contact with the pure ammonia can shortenthe life of the hydrogen separation membrane 38. Therefore, in someembodiments the membrane is not placed where the ammonia first entersthe hydrogen membrane reactor 12. In such embodiments, the hydrogenmembrane includes a non-membrane leader portion of a suitable length toensure that the product gas inside the reactor first contacts themembrane only after the ammonia concentration in the reactor has beenreduced to ppm levels. For example, in a generator designed to providesufficient hydrogen to generate 20 watts of power, a palladium-ceramiccomposite membrane with less than about 5 cm² of membrane is sufficientto efficiently separate hydrogen from synthesis gas. In this alternativeembodiment, there is a single hydrogen exhaust channel in fluidcommunication with the relatively small membrane surface.

The top plate 32 separates the hydrogen exhaust zone 40 from aninsulating panel 42, while the bottom plate 34 separates the combustionchamber 13 b from an insulating panel 46. As seen in FIG. 3, inpreferred embodiments, the sides of the reactor are insulated, as well,with insulating side panels 46. Preferably, the insulating panels arefabricated from an aerogel material, which can provide excellentinsulation and is a very lightweight material.

FIG. 3 is a cross-sectional view of a preferred embodiment of thehydrogen membrane reactor 12. FIG. 4 is an exploded isometric view ofthe different layers of the hydrogen membrane reactor of FIG. 3, withthe side insulative layers omitted for clarity. FIGS. 3 and 4 illustratea plurality of combustion channels 50 extending radially from theadjacent surface 37 b of the separation plate 36. The combustionchannels are formed in a thin metal combustion plate or sheet 52interposed between the bottom plate 34 and the separation plate. Aplurality of hydrogen exhaust channels 54 extending radially from thefirst surface 39 a of the hydrogen membrane 38 are formed in a thinmetal hydrogen exhaust channel plate or sheet 56 interposed between thetop plate 32 and the hydrogen membrane. A plurality of reaction channels58 extending radially from the second surface 39 b of the hydrogenmembrane are formed in a thin metal reaction channel plate or sheet 59interposed between the bottom plate 34 and the separation plate. Inpreferred embodiments, these channels are formed in the thin metalsheets, either by micromachining or stamping. It should also beunderstood, that the specific orientation and configuration ofmesochannels in any of these elements is not critical, so long as forthe orientation selected, the efficiency and processing benefitsprovided by mesochannels are retained (i.e., small-dimensioned fluidchannels that provide excellent fluid flow and high heat transferrates).

The dimensions of the channels 50, 54, and 58 within the hydrogenmembrane reactor are preferably “meso” in scale. Meso scale systems fallbetween the macro scale systems associated with traditional full-sizedsystems, like those used in the petrochemical industry, and the microscale systems commonly encountered in the microelectronics industry.That is, preferably the height and or width of each channel is between0.01 mm and 10 mm, and is more preferably between 0.5 mm and 5 mm.

Regardless of which fuel is employed, thermal energy is required todrive the desired reaction. One way of reducing the thermal energyrequired to drive the hydrogen generating reactions is to include anappropriate reaction catalyst within the hydrogen membrane reactor 12.Thus, in preferred embodiments, the reaction zone 41 includes a reactioncatalyst to facilitate the chemical transformation of fuel intohydrogen. In general, the catalysts are reaction specific, and theselection of the particular catalyst to be employed will be based, inpart, on whether the selected fuel is ammonia or a liquid hydrocarbon.

Moreover, the characteristics of specific catalysts (and any requiredcatalyst support, such as alumina) affect the design of the reactor. Forexample, for a given volume, different catalysts will require differentflow rates to achieve the same conversion efficiency. Similarly, for agiven flow rate, different catalysts will require different reactorvolumes to achieve the same conversion efficiency.

Also, useful reaction catalysts function under different temperatureconditions, each catalyst having a characteristic “light-off”temperature (a minimum required temperature below which little or nocatalytic activity is observed), as well as a characteristic optimaltemperature. These temperature parameters affect a specific reactordesign by defining minimum and Optimum reactor temperatures. Thus, thecatalyst selected will influence optimal temperature conditions, flowrates, and reactor volumes.

The temperature conditions, in particular, determine the type ofmaterials that can be used in fabricating the reactor (conventionalmetals for temperatures less than 650° C., or refractory metals forhigher temperatures). Relatively low temperature reactors (operating atless than 650° C.) and appropriate catalysts are a particularly usefuland preferred combination.

Preferred reaction catalysts for ammonia disassociation at temperaturesless than 650° C. include ruthenium-based catalysts, often provided asruthenium dispersed in an aluminum oxide support matrix, such as Type146, available from Johnson Matthey. By utilizing a reactor temperatureof less than 650° C., very high surface area catalyst substrates, suchas gamma alumina and nanophase titania can be employed. Temperatures inexcess of 800° C. often cause these materials to sifter or undergo phasechanges that result in a much lower substrate surface area andcorrespondingly lower catalyst activity. Preferably, the rutheniumammonia disassociation catalyst is dispersed in either a gamma aluminaor nanophase titania matrix when a packed catalyst bed is utilized.

Since oxygen is included with the ammonia to support the initialcombustion, in some embodiments catalysts less oxygen sensitive thanruthenium-based catalysts are employed. Moreover, when assemblingreactors containing oxygen-sensitive catalysts (i.e., by brazing the topcover to the reactor core) it may be beneficial to provide a reducingatmosphere in order to prevent the catalysts from oxidizing.

Nickel-based catalysts, such as Katalco 27-7™ (available fromICI/Katalco of the UK) are also preferred ammonia dissociationcatalysts. However, the nickel catalyst requires a longer residence timethan the ruthenium catalyst to achieve similar conversion efficiency.The ruthenium catalyst has a residence time that is approximatelyone-tenth that of the nickel catalyst.

Other suitable ammonia dissociation catalysts include iron oxide,rhodium, iridium, and rhenium catalysts.

Preferred embodiments additionally contain a combustion catalyst withinthe combustion chamber 13 b. The combustion catalyst is employed toenable the fuel to be more readily combusted to generate the thermalenergy required to drive the hydrogen generation reaction. Catalyticcombustion is a unique chemical reaction differing from open flamecombustion, in that a catalyst is used to ensure an efficient combustionprocess occurs at a lower temperature.

In particular, without such a combustion catalyst, ammonia is difficultto ignite and sustain combustion in air. For this reason, a combustioncatalyst is required to enable ambient air to be employed when ammoniais used as the fuel. Preferred ammonia combustion catalysts includeplatinum-rhodium alloys. Similarly, by introducing platinum into ahydrocarbon/oxygen combustion process, it is possible to increase thepercentage of fuel burned from less than 85% to about 98%.

The catalysts can be incorporated by any suitable method. For example,the catalysts included in reaction channels 58 and combustion channels50 can either be incorporated as packed beds in each channel, or as athin layer or coating deposited on the internal surfaces of the thinmetal sheet comprising the channels.

Any suitable means can be employed to trigger the combustion reaction.In a preferred embodiment, a glow plug (not shown) is used. The glowplug is essentially a nichrome or other metallic element that is incontact with the combustion catalyst in the combustion chamber of thehydrogen membrane reactor 12. A small battery (not shown) deliverscurrent to the wire, which increases the temperature of the combustioncatalyst to a “light-off” temperature, i.e., to that temperature atwhich the ammonia combustion catalyst will facilitate the combustion ofammonia. In an alternative embodiment, a spark-based igniter is used.While the spark-based igniter offers the advantage of not requiring abattery, the air/fuel mixture must be much more tightly controlled toenable spark-based ignition to occur. Once the combustion is initiated,the process is self sustaining as long as there is sufficient fuel andoxygen, and as long as the temperature remains above 650° C.

The fuel heat exchanger 26 is disposed in the fuel supply line 20 and inthe combustion by-products supply line 24 to provide a thermalconnection between the fuel and the combustion by-products. The oxygenheat exchanger 28 is disposed in the oxygen supply line 22 and thereaction products line 25 to provide a thermal connection between theoxygen and the reaction products. The fuel heat exchanger extracts heatfrom the hot reaction product gases exiting hydrogen membrane reactorand preheats the fuel entering the reactor. Similarly, the oxygen heatexchanger extracts heat from the hot reaction product gases exitinghydrogen membrane reactor and preheats the oxygen entering the reactor.

In an alternative embodiment, the fuel heat exchanger 26 is disposed inthe reaction product supply line 25 to provide a thermal connectionbetween the fuel and the reaction products, while the oxygen heatexchanger 28 is disposed in the combustion by-products line 24 toprovide a thermal connection between the oxygen and the combustionby-products. With both embodiments, the materials entering the hydrogenmembrane reactor 12 are preheated to temperatures approaching theoperating temperature of the reactor, so that additional fuel is notconsumed to heat the reactants.

Because the vaporization process is an endothermic process (energy isconsumed in the process), the liquid, or liquefied gaseous, fuel exitingthe fuel tank 14 advantageously vaporizes in the fuel heat exchanger 26.For example, in returning to the gaseous state, liquefied ammonia (orother liquid fuel) absorbs substantial amounts of heat from itssurroundings (i.e. one gram of ammonia absorbs 327 calories of heat).Therefore, when the vaporization occurs in heat exchanger 14, itobviates the need for additional fuel to be consumed in the reactor togenerate the thermal energy that would otherwise have been necessary todrive the vaporization process. Thus, what would otherwise be waste heatis employed to vaporize the liquefied ammonia (or other fuel).

The fuel and oxygen heat exchangers 26 and 28 are preferablycounterflow-type heat exchangers. In some embodiments, the heatexchanges are tube-in-tube type devices. In other embodiments, the heatexchangers are stacked plate-type heat exchangers. In those embodimentswhere the heat exchanger is a stacked plate type heat exchanger, it ismost preferable that the channels running between the plates have mesoscale dimensions. While not specifically shown, both heat exchangers areinsulated, so that little thermal energy is lost.

FIG. 5 is an exploded isometric view of a stacked plate-type mesochannelheat exchanger 60 for use in the present invention. The heat exchangerincludes a first plate 62 and a second plate 64 encased in a housing(not shown). Aligned through each plate are a first fluid, inlet, e.g.,a fuel inlet or an oxygen inlet, 66, a first fluid outlet 68, a secondfluid inlet, e.g., a combustion by-product or a reaction product inlet,70, and a second fluid outlet 72. The first fluid flows in through thefirst fluid inlet, than flows through a plurality of mesochannels 74formed on the surface of the side of the first plate opposite the secondplate, and then out through the first fluid outlet. The second fluidflows in through the second fluid inlet, then flows in directionopposite to the direction of flow of the first fluid, through aplurality of mesochannels 76 formed on the surface of the side of thesecond plate adjacent the first plate, and then out through the secondfluid outlet through.

In one embodiment, such heat exchangers are produced from 25 micronstainless steel foils, which axe bonded using electroplating. Ceramicheat exchangers of a similar design can also be employed. Suchmesochannel heat exchangers have up to 97% efficiency, while at the sametime being relatively light-weight. The pressure drop is extremelylow—approximately 2″ of water column.

In those embodiments, where expediency in switching from ammonia tohydrocarbon fuels (and vice versa) is desired, the fuel tank 12 and theheat exchangers 26 and 28 are fabricated so that they are compatiblewith both ammonia and hydrocarbon fuels. In alternative embodiments,where it is desired to minimize the cost of the components, differentfuel tanks and heat exchangers are used for different fuels. Forexample, not all seal materials are compatible with both ammonia andhydrocarbons. Some, generally more expensive seal materials arecompatible with both. Furthermore, since ammonia and the water producedby combustion of ammonia form a corrosive mixture, corrosion resistantmaterials should be used, instead of stainless steel. Furthermore, it ispreferable for such components to be able to be reused. That is, somematerials may be chemically compatible with the fuel for only a shortperiod of time. The hydrogen generator preferably is a reusable system,and thus the fuel supply and the fuel heat exchanger are preferablyadapted to be used with the fuel for extended cycles. Therefore, ratherthan employing expensive materials for all such components, it may bebeneficial to fabricate different heat exchangers and different fuelsupplies specifically adapted to be compatible with a selected fuel(ammonia or hydrocarbon).

The hydrogen generator 10 also includes an air injector pump 78 disposedin the oxygen supply line 22 between the oxygen heat exchanger 30 andthe hydrogen membrane reactor and in the tail gas supply line 23. Theinjector pump conveys both the tail gas exiting the reaction chamber andthe air from the oxygen supply into the combustion chamber of hydrogenmembrane reactor 12.

Preferably, the hydrogen generator 10 will generate hydrogen on demandand in those embodiments where the hydrogen is to be used immediatelyafter it is generated the hydrogen reservoir 18 is not required.However, there are inefficiencies inherent in a hydrogen generatingcycle that comprises a series of short periods of operation followed bylong periods of inactivity, because during the start up phase, the fuelis being used to bring the system up to an operating temperature ratherthan for generating hydrogen. Therefore, in some embodiments, thehydrogen reservoir is employed to store hydrogen not currently required,so that while the system is at operating temperature, the fuel can beemployed to generate hydrogen for later use, rather than to bring thesystem to operating temperature.

As shown in FIG. 1, in those embodiments employing ammonia as a fuel andwhere the hydrogen gas is to be used to power an H/AFC, it is preferredto include an ammonia adsorbent supply 80 in fluid connection with thereaction product line 26. H/AFCs can be adversely affected by even traceamounts of ammonia, so the adsorbent is capable of removing any residualammonia contained within the hydrogen exiting hydrogen membrane reactor12. Under ideal conditions, a properly designed and functioning hydrogenmembrane reactor will not allow any ammonia to pass through themembrane. However, microscopic manufacturing defects, post manufacturepunctures, or poor sealing along the edges of a hydrogen membrane canenable a small amount of ammonia to contaminate the hydrogen stream.

In embodiments where the hydrogen is used for purposes that are not assensitive to residual ammonia, such as welding or metal treating, theabsorbent supply may not be necessary. Similarly, if manufacturingdefects, punctures, and sealing deficiencies are uncommon, then ammoniaadsorbent supply will not be required.

The adsorbent within the adsorbent supply 56 should remove substantiallyall (leaving less than 1 ppm) of the residual ammonia from the hydrogenproduct. Preferred adsorbents include carbon and modified carbonadsorbents. Most preferred adsorbents include carbon whose surface hasbeen impregnated to include bound acid molecules. The acid thus boundneutralizes the residual ammonia. At a minimum, the most preferredadsorbent has 2 millimoles of strong acid adsorption sites per gram ofcarbon, and the most preferred adsorbent can have up to 5 millimoles pergram of carbon.

For embodiments in which the fuel cell 31 is added to the system togenerate electricity from the hydrogen produced, the preferred fuel cellis a PEM fuel cell. Embodiments that incorporate a battery 82 are alsocontemplated. Such systems can provide useful power even when no oxygenis available. Normally, oxygen is required by the hydrogen generator 10to react with the fuel in the hydrogen membrane reactor 12. Oxygen isalso needed as a fuel for the reaction that occurs in the fuel cell 31.However, in some embodiments, the system first can be operated in anaerobic environment for a period of time sufficient to generatesufficient hydrogen for the fuel cell to produce enough electricity tobring the battery to a substantially charged state. Then the system canbe placed in an anaerobic environment (such as underwater) and still becapable of supplying electrical power from the battery for a period oftime. Note that the incorporation of batteries increases the system sizeand weight, and somewhat decreases the energy density of the system;accordingly, this embodiment is most beneficially employed whenanaerobic conditions are anticipated. Preferably, such a system will beprepared for use with a fully charged battery and a full fuel supply 14,so that fuel from the fuel supply does not need to be used to initiallycharge the battery.

Turning now to the operation of the hydrogen generator 10, the systemhas both start up and steady state operational modes. The start up modeis the period in which fuel is burned to bring the reactor 12, and morespecifically, the reaction catalyst, up to the required reactiontemperature. During this start up period, little or no hydrogen isgenerated. The steady state mode of operation represents the time afterthe reactor has reached operating temperature, and the fuel is beingprimarily converted to hydrogen. In preferred embodiments, during thesteady state mode, thermal energy is generated by combusting theby-products that are separated from the hydrogen using the hydrogenmembrane. The by-products, or tail gas, are combined with air andburned, to extract the maximum thermal energy from the fuel.

FIG. 6 shows fluid flows for the hydrogen generator 10 in the start upphase. Referring specifically to an embodiment where liquefied ammoniais the fuel, liquefied ammonia exits fuel tank 14 and flows through fuelsupply line 20 into fuel heat exchanger 28. At start up, the fuel heatexchanger is cold, so no preheating of the ammonia occurs. However, theliquefied ammonia substantially volatilizes at room temperature withoutpreheating, and so ammonia vapor flows through the fuel supply line intothe reaction chamber (not separately shown) of the hydrogen membranereactor 12. Because the reactor is cold (room or ambient temperatureverses a preferred operating temperature of 650° C.) no disassociationoccurs, and the “tail gas” exiting the reaction chamber through the tailgas supply line 23 is ammonia. That ammonia is then fed into thecombustion chamber (not separately shown), along with ambient airtransported through the oxygen supply line 22 from the oxygen supply 16.At this time, the oxygen heat exchanger 30 is also at ambienttemperature, so that no preheating of air introduced into the combustionchamber occurs.

In the combustion chamber of hydrogen membrane reactor 12, the ammoniaand air, in the presence of the combustion catalyst, are ignited. As thereactor initially heats up, combustion by products exiting the reactorthrough combustion by-product line 24 cause the fuel heat exchanger 28to begin to heat up as well. The heat, in turn, causes the ammoniatraveling through fuel supply line 20 to be preheated, further addingthermal energy to the reactor. The start up phase continues until thecatalyst is heated up to its own light off temperature. At that point,the ammonia disassociation reaction is enabled, and the system enters asteady state.

In the steady state, as illustrated in FIG. 7, ammonia entering thereaction zone of the reaction chamber (not separately shown) though fuelsupply line 20 disassociates into hydrogen and nitrogen as illustratedby Equation 1. The majority of the hydrogen passes through the hydrogenmembrane (not shown) and travels through the hydrogen exhaust channels(not separately shown) out of the membrane reactor through reactionproduct line 26. The hydrogen membrane allows hydrogen to diffuse acrossthe membrane, eliminating the need for a further separation step toobtain a relatively pure hydrogen stream. Besides separating the desiredhydrogen stream from other reaction products, the hydrogen membranefavorably affects the kinetics of the hydrogen generation reaction. Bycontinually removing hydrogen from the reaction zone, the membranecauses an imbalance in the reaction kinetics that drives the conversionof more fuel into hydrogen in response to this imbalance. Thisconversion further increases the efficiency of the process, as withoutsuch a driving force, additional thermal energy would be required todrive the hydrogen generation reaction.

The hot hydrogen passes through the hydrogen membrane, into the hydrogenexhaust zone and then out of the hydrogen membrane reactor 12 throughthe reaction product line 26. The hot hydrogen enters oxygen heatexchanger 30 and is cooled by the ambient air transported through theoxygen supply line 22, which in turn is preheated before enteringhydrogen the hydrogen membrane reactor. The tail gas now includesprimarily nitrogen with traces of unreacted ammonia and traces ofhydrogen that did not pass through the hydrogen membrane. The tail gashas some fuel value (due to the traces of ammonia and hydrogen) andenters the combustion chamber of hydrogen membrane reactor, wherecombustion of the tail gas provides sufficient thermal energy tomaintain the required thermal conditions in hydrogen membrane reactorfor self-sustaining disassociation and combustion reactions to occur, solong as the ammonia from ammonia storage tank 14 is provided.

FIG. 8 illustrates fluid flows for an alternative hydrocarbon generator100 based on a hydrocarbon steam reformation reaction. In thisembodiment, the hydrogen produced is used to power a fuel cell (or forother purposes as described above) while the CO is combusted to providethermal energy to sustain the steam reforming reaction.

The hydrogen generator 100 shares many features with the hydrogengenerator 10 and similar elements are identified with similar numbers.The difference is that hydrogen generator 100 also incorporates a watersupply system to provide steam for the steam reforming reaction. Thewater supply system includes a hydrocarbon fuel tank 140, a waterstorage tank 142, and a hydrocarbon/water pump 144. If a pressurizedhydrocarbon (such as natural gas or propane) is employed as the fuel,the pressure alone would be enough to drive the fuel through thehydrogen generator. However, if a liquid hydrocarbon, such as JP-8 isemployed, the pump will be required. Regardless, the pump provides amotive force to drive water from the water storage tank though fluidsupply line 120 into the hydrogen membrane reactor 12. A fuel heatexchanger 28 operably connected to the fuel supply line and a combustionby-product line 24 is included to transform the water into steam and topreheat the hydrocarbon fuel.

Hydrogen generator 100 includes a hydrogen membrane reactor 12 havingtwo separate chambers (not shown), a reaction chamber in a heat exchangerelationship with a combustion chamber. In a preferred embodiment, thereaction chambers each incorporate mesoscale channels to enhance thereaction efficiencies.

The reaction chamber incorporates a steam reforming catalyst, while thecombustion chamber incorporates a catalyst to facilitate the combustionof the selected hydrocarbon fuel. Catalysts for steam reforming ofhydrocarbons and combustion of hydrocarbons are readily available from avariety of sources. For example, the catalyst division of JohnsonMatthey, in Wayne, Pa., provides suitable catalysts. The reactioncatalysts have characteristic “light-off” temperatures, as well as acharacteristic optimal temperature. These temperature parameters affecta specific reactor design by defining minimum and optimum reactortemperatures. In a preferred embodiment, the desired reactor temperaturewill be less than 650° C., so that conventional metals (rather than hightemperature refractory metals) can be used to fabricate the hydrogenmembrane reactor. In one embodiment, the catalysts are incorporated aspacked beds, while in another embodiment the catalysts are deposited onsurfaces of the reaction chamber and the combustion chamber.

In some embodiments, the hydrogen generator includes a water recoverysystem, to reduce the amount of water required. This feature isparticularly advantageous if a small and compact system is required.Such a water. recovery system is in fluid communication with the pump144, and includes a recovered water return line 148 that is in fluidcommunication with the fuel heat exchanger 28, such that the waterfraction from the cooled combustion products exiting the fuel heatexchanger is recycled through the recovered water reservoir 148, whileother combustion products are simply exhausted.

FIG. 9 shows fluid flows for the hydrogen generator 100 in a start upphase. The hydrocarbon fuel from hydrocarbon storage tank 140 istransported through the fuel supply line 120 (using the fuel pump 144 ifa non-pressurized fuel is employed) into the fuel heat exchanger 28.Because the fuel heat exchanger is cold at startup, steam generation andhydrocarbon preheating cannot occur, so that water for steam generationis not required. Also, because hydrogen membrane reactor 12 is cold(ambient temperature versus 650° C.) no steam is yet required for steamreformation.

The hydrocarbon first enters the reaction chamber. At start up, no steamreformation can occur, and the “tail gas” exiting the reaction chamberthough tail gas supply line 23 will be pure hydrocarbon. Thathydrocarbon is then fed through the tail gas supply line into thecombustion chamber, along with ambient air transported through oxygensupply line 24 from oxygen supply 16. At this time, the oxygen heatexchanger 30 is also at ambient temperature, so that preheating of theair introduced into the hydrogen membrane reactor 12 does not yet occur.

In the combustion reaction chamber of hydrogen membrane reactor 12, thehydrocarbon and air, in the presence of the combustion catalyst, areignited. As the reactor initially heats up, combustion products exitingthe reactor cause the fuel heat exchanger 28 to begin to heat up aswell, which causes the hydrocarbon fuel from storage tank 140 to bepreheated, further adding thermal energy to the reactor. The start upphase continues until the reaction catalyst is heated to its light offtemperature. At that point, water is released from storage tank 142. Ifpump 144 is not yet on, it is now energized. The oxygen heat exchanger30, now hot due to the heat of the combustion products exiting thecombustion chamber, transforms the water to steam. The steam reformationreaction is now enabled, and the system enters a steady state.

In the steady state, as illustrated in FIG. 10, steam and hydrocarbonsentering the reaction are reformed into hydrogen and carbon monoxide.The majority of the hydrogen exits the reaction zone by passing throughthe hydrogen membrane, into the hydrogen exhaust zone, and then out ofthe hydrogen membrane reactor through the reaction product line 26. Thishot hydrogen enters oxygen heat exchanger 30 and is cooled by ambientair, which in turn is preheated before entering the combustion chamber.The tail gas now includes primarily carbon monoxide with traces ofunreformed hydrocarbons, and traces of hydrogen that did not passthrough the hydrogen membrane and has significant fuel value. The tailgas enters the combustion chamber, where combustion of the tail gasprovides sufficient thermal energy to maintain the required thermalconditions in the hydrogen membrane reactor for self sustaining steamreformation and combustion reactions to occur, as long as hydrocarbonfuel and steam are provided.

In a preferred embodiment, a hydrogen generating system in accordancewith the present invention will include real-time, automated, and lowpower process control elements, including gas sensor technology, toprovide an automated system that requires minimal user interaction.Miniature real-time gas sensors and miniature flow control valves can beincorporated into compact systems. Preferably, a programmablemicroprocessor is used to digitize sensor inputs and actuate flowcontrol components. To minimize power consumption, such process controlelements require low power. Lightweight components for pressure andtemperature measurements are commercially available. Preferably, theonly composition sensor required by the process control system is anoxygen sensor, which is commercially readily available, having beendeveloped for the automotive industry.

In some embodiments, the hydrogen generator is designed to operate in asubmerged environment for short periods, with an energy density of 2000watt hours/kg. The performance requirements for such embodiments arebased on a three-day period, requiring a total energy of approximately1500 watt hours. The total hydrogen generator weight is less than 1 kg(about 720 g). Further, the hydrogen generator provides a 20 wattaverage power output level. Peak sustainable output is about 30 watts.To meet these energy requirements, the hydrogen generator is designed toproduce a total of approximately 75 grams of hydrogen.

Table I shows the weight of fuel required by such designs, given theconversion efficiency provided.

TABLE I Fuel Weight Requirements for Three-Day Period Fuel Est.Efficiency of Hydrogen Generator Mass of Fuel Ammonia 95% 499 JP-8 80%245

FIG. 11 illustrates an ammonia-decomposition-based hydrogen generator200 designed to produce 82 grams of hydrogen at a maximum productionrate of 300 sccm, and a minimum production rate of 30 sccm. It is anadvantage of the hydrogen generator that there are no rotating parts,such as fans, blowers or pumps. The absence of such components reducesnoise, reduces parasitic power consumption, and increases reliability.

Based on a complete analysis, accounting for chemical equilibrium, massbalances, energy balances and assumed heat exchanger efficiencies of95%, mass flow rates are indicated that correspond to a hydrogenproduction rate of 235 sccm. This hydrogen generation rate is requiredto produce 20 watts of electric power, the desired average output forthis system.

Table II reports the mass flow rates, compositions, temperatures, andpressures are presented at each point in the process identified in FIG.11.

TABLE II Process Parameters at Steady State and Full Hydrogen OutputMass Process Pressure Temperature Composition Flow Point (psia) (C.)(mole fraction) (g/h) 1 60 25 NH₃ = 1.0 7.2 2 60 577 NH₃ = 1.0 7.2 3 15600 H₂ = 1.0 1.09 4 15 66 H₂ = 1.0 1.09 5 14.7 25 N₂ = 0.79/O₂ = 0.216.2 6 14.7 571 N₂ = 0.79/O₂ = 0.21 6.2 7 60 600 N₂ = 0.69/H₂ = 0.30/NH₃< 0.01 6.2 8 15 594 N₂ = 0.74/O₂ = 0.1/H₂ = 0.16 12.4 9 15 600 N₂ =0.8/O₂ = 0.02/H₂O = 0.18 13.1 10 14.7 350 N₂ = 0.8/O₂ = 0.02/H₂O = 0.1813.1

Table III reports the size and weight of the various components.

TABLE III Size and Mass Estimates for Key Components Component Size(cm³) Mass (g) Reactor 2 × 2 × 8 = 32 40 Ammonia thermal exchanger 1 × 2× 8 = 16 20 Air thermal exchanger 1 × 2 × 8 = 16 16 Packaging, plumbingand controls 40 50

FIG. 12 illustrates a hydrocarbon steam reformation-based hydrogengenerator 300. The generator is designed to produce 80 grams of hydrogenat a maximum production rate of 200 sccm. The only moving parts are theliquid fuel and water pumps. The absence of blowers reduces noise,reduces parasitic power consumption, and increases reliability.

Based on a complete analysis, accounting for chemical equilibrium, massbalances, energy balances and assumed heat exchanger efficiencies of96%, mass flow rates are indicated that correspond to a hydrogenproduction rate of 200 sccm.

Table IV reports the mass flow rates, compositions, temperatures andpressures are represented at each point in the process identified inFIG. 12.

TABLE IV Process Parameters at Steady State with Hydrogen Output for 20Watts Power Mass Process Pressure Temperature Flow Point (psia) (C.)Composition (mole fraction) (g/h) 1 14.7 25 HC = 1.0 3.33 2 60 25 HC =.04/H₂O = .96 11.9 3 60 600 HC = .04/H₂O = .96 11.9 4 15 600 H₂ = 1.01.09 5 15 25 H₂ = 1.0 1.09 6 14.7 580 N₂ = 0.79/O₂ = 0.21 12.3 7 14.7600 N₂ = 0.79/O₂ = 0.21 12.3 8 60 600 CO₂ = .38/CO = .19/H₂O = .19/ 10.8H₂ = .24 9 15 580 CO₂ = .19/CO = .09/H₂O = .21/ 23.9 H₂ = .12/N₂ = .4010 14.7 600 N₂ = .80/CO₂ = .28/H₂O = .32 24.9 11 14.7 70 N₂ = .57/CO₂ =.40/H₂O = .03 20.3 12 14.7 70 H₂O = 1.0 4.64

Table V reports the size and weight of the various components.

TABLE V Size and Mass Estimates for Key Components Component Size (cm³)Mass (g) Reactor 2 × 4 × 8 = 64 60 Fuel/water thermal exchanger 1 × 4 ×8 = 32 30 Air thermal exchanger 1 × 4 × 8 = 32 30 Packaging, plumbingand controls 60 200

Although the present invention has been described in connection with thepreferred form of practicing it, those of ordinary skill in the art willunderstand that many modifications can be made thereto without departingfrom the spirit of the present invention. Accordingly, it is notintended that the scope of the invention in any way be limited by theabove invention.

1. A hydrogen generator comprising: a hydrogen membrane reactor having acombustion chamber in a fluid connection with and in a heat exchangerelationship with a reaction chamber, wherein the hydrogen membranereactor comprises a top plate, a bottom plate, and a separation platehaving first and second opposing surfaces, the top plate and the firstsurface of the separation plate together defining the reaction chamber,the bottom plate and the second surface of the separation plate togetherdefining the combustion chamber, a hydrogen separation membrane havingfirst and second opposing surfaces disposed between the top plate andthe separation plate, the top plate and the first surface of thehydrogen separation membrane together defining a hydrogen exhaust zoneand the separation plate and the second surface of the hydrogenseparation membrane together defining a reaction zone; the combustionchamber comprises a plurality of combustion channels extending from thesurface of the separation plate, the combustion channels creating afluid path through the combustion chamber; the hydrogen exhaust zonecomprises a plurality of hydrogen exhaust channels extending from thefirst surface of the hydrogen membrane, creating a fluid path throughthe hydrogen exhaust zone; and the reaction zone comprises a pluralityof reaction channels extending from the second surface of the hydrogenmembrane, creating a fluid path through the reaction zone; a fuelsupply; a fuel supply line for transporting fuel from the fuel supply tothe reaction chamber; an oxygen supply; an oxygen supply line fortransporting oxygen from the oxygen supply to the combustion chamber; atail gas supply line for transporting tail gases from the reactionchamber; a combustion by-product line for transporting combustionby-products from the combustion chamber; and a reaction product line fortransporting hydrogen from the reaction chamber; and wherein the tailgas supply line makes a fluid connection between the reaction chamberand the combustion chamber.
 2. A hydrogen generator in accordance withclaim 1 wherein the height and width of each of the combustion channels,the hydrogen exhaust channels, and the reaction channels is between 0.01mm and 10 mm.
 3. A hydrogen generator in accordance with claim 1 whereinthe height and width of each of the combustion channels, the hydrogenexhaust channels, and the reaction channels is between 0.5 mm and 5 mm.4. A hydrogen generator in accordance with claim 1 wherein the tail gassupply line makes a fluid connection between the reaction zone and theoxygen supply line.
 5. A hydrogen generator in accordance with claim 1further comprising a fuel heat exchanger operably connected to the fuelsupply line and one of the combustion by-product line or the reactionproduct line.
 6. A hydrogen generator in accordance with claim 5 whereinthe fuel heat exchanger is a stacked-plate-type heat exchanger havingchannels with a height and a width between about 0.01 mm and 10 mmrunning between the stacked plates.
 7. A hydrogen generator inaccordance with claim 1 further comprising an oxygen heat exchangeroperably connected to the oxygen supply line and one of a combustionby-product line or a reaction product supply line.
 8. A hydrogengenerator in accordance with claim 7 wherein the oxygen heat exchangeris a stacked-plate-type heat exchanger having channels with a height anda width between about 0.01 mm and 10 mm running between the stackedplates.
 9. A hydrogen generator in accordance with claim 1 furthercomprising a fuel heat exchanger operably connected to the fuel supplyline and the combustion by-product line and an oxygen heat exchangeroperably connected to the oxygen supply line and a reaction productsupply line.
 10. A hydrogen generator in accordance with claim 1 furthercomprising a hydrogen reservoir in fluid connection with the reactionproduct supply line.
 11. A hydrogen generator in accordance with claim 1further comprising a hydrogen fuel cell in fluid connection with areaction product supply line.
 12. A hydrogen generator in accordancewith claim 1 wherein the fuel supply is an ammonia supply.
 13. Ahydrogen generator in accordance with claim 1 further comprising acombustion catalyst in the combustion chamber.
 14. A hydrogen generatorin accordance with claim 1 further comprising a combustion catalystpacked in or coated on an internal surface of the combustion channels.15. A hydrogen generator in accordance with claim 1 further comprising areaction catalyst in the reaction chamber.
 16. A hydrogen generator inaccordance with claim 1 further comprising a reaction catalyst packed inor coated on the internal surfaces of the reaction channels.
 17. Ahydrogen generator in accordance with claim 13 further comprising anammonia adsorbent supply in fluid communication with the reactionproduct line.
 18. A hydrogen generator in accordance with claim 1wherein the fuel supply is a hydrocarbon supply.
 19. A hydrogengenerator in accordance with claim 18 wherein the hydrocarbon supply ismethanol, propane, butane, or kerosene supply.
 20. A hydrogen membranereactor comprising a top plate, a bottom plate, and a separation platehaving first and second opposing surfaces, the top plate and the firstsurface of the separation plate together defining the reaction chamber,the bottom plate and the second surface of the separation plate togetherdefining the combustion chamber, the combustion chamber having aplurality of combustion channels extending radially from the surface ofthe separation plate, the combustion channels creating a fluid paththrough the combustion chamber, a hydrogen separation membrane havingfirst and second opposing surfaces disposed between the top plate andthe separation plate, the top plate and the first surface of thehydrogen separation membrane together defining a hydrogen exhaust zone,the hydrogen exhaust zone having a plurality of hydrogen exhaustchannels extending radially from the first surface of the hydrogenmembrane, the hydrogen exhaust channels creating a fluid path throughthe hydrogen exhaust zone, and the separation plate and the secondsurface of the hydrogen separation membrane together defining a reactionzone; the reaction zone having a plurality of reaction channelsextending radially from the second surface of the hydrogen membrane, thereaction channels creating a fluid path through the reaction zone; afuel inlet into the reaction zone; an oxygen inlet into the combustionchamber, a tail gas outlet out of the reaction zone; a hydrogen outletout of the hydrogen exhaust zone; and a by-product outlet out of thecombustion chamber wherein the tail gas outlet makes a fluid connectionbetween the reaction chamber and the combustion chamber.
 21. A hydrogenmembrane reactor in accordance with claim 20 wherein the height andwidth of each of the combustion channels, the hydrogen exhaust channels,and the reaction channels is between 0.01 mm and 10 mm.
 22. A hydrogenmembrane reactor in accordance with claim 20 wherein the height andwidth of each of the combustion channels, the hydrogen exhaust channels,and the reaction channels is between 0.5 mm and 5 mm.
 23. A hydrogenmembrane reactor in accordance with claim 21 further comprising acombustion catalyst packed in or coated on the internal surfaces of thecombustion channels.
 24. A hydrogen membrane reactor in accordance withclaim 21 further comprising a reaction catalyst packed in or coated onthe internal surfaces of the reaction channels.
 25. A hydrogen generatorcomprising: a hydrogen membrane reactor including a combustion chamberhaving an inlet and an outlet in a heat exchange relationship with areaction chamber having an inlet and an outlet; wherein the hydrogenmembrane reactor comprises a top plate, a bottom plate, and a separationplate having first and second opposing surfaces, the top plate and thefirst surface of the separation plate together defining the reactionchamber, the bottom plate and the second surface of the separation platetogether defining the combustion chamber, a hydrogen separation membranehaving first and second opposing surfaces disposed between the top plateand the separation plate, the top plate and the first surface of thehydrogen separation membrane together defining a hydrogen exhaust zoneand the separation plate and the second surface of the hydrogenseparation membrane together defining a reaction zone; the combustionchamber comprises a plurality of combustion channels extending from thesurface of the separation plate, the combustion channels creating afluid path through the combustion chamber; the reaction zone comprises aplurality of reaction channels extending from the second surface of thehydrogen membrane, creating a fluid path through the reaction zone; afuel supply; a fuel supply line fluidly connecting the fuel supply tothe reaction chamber inlet, an oxygen supply; an oxygen supply linefluidly connecting the oxygen supply to the combustion chamber inlet; atail gas supply line making a fluid connection between the reactionchamber outlet and the combustion chamber inlet; a combustion by-productline making a fluid connection with the combustion chamber fortransporting combustion by-product from the combustion chamber; and areaction product line for transporting hydrogen from the reactionchamber.